1. Field of the Invention:
This invention relates to a holding device for attachment of a filter, particularly one which is relatively thin, to an optical instrument such as interchangeable lens or intermediate tube.
2. Description of the Prior Art:
In single lens reflex cameras, interchanging the objective lens enables strong and weak perspectives and changing of the image angle to be effected so that even when photographing the same scene, different pictures can be obtained. Therefore, the use of a great number of interchangeable lenses of different focal lengths enables the photographer to make a desired selection. Among the interchangeable lenses, the super wide angle lens of emphatic perspective encounters many opportunities to be used, and a great many excellent lenses have been developed and are available in the market.
However, when considering using a filter with the super wide angle lens, the attachment thereof to the front end of the lens mounting in the case of normal and telephoto lenses gives rise to problems in that the filter becomes large and expensive. Also, because the curvature of the exposed surface of the front lens member is very sharp as the angular field of view is widest, there is a high possibility of mechanical interference between the filter and the front lens member. It has, therefore, been common practice in the art that a few filters are provided in the interior of the lens system in changeable positions, or that a special filter is fixed to the rear wall of the lens mounting. In any case, there is a drawback in that the number of different filters usable is limited.
In the case where the above-mentioned drawback is eliminated by using gelatin filters, which are available in a great number of types and are very cheap, because of the lack of an anti-reflection coating on the filter, ghost and flare are produced, thus creating an alternate drawback preventing good photographs from being taken.